A detecting instrument based on ion migration spectrum (IMS) technologies may be used for detecting trace-level prohibited articles such as explosives, drugs and toxic chemicals, etc. Due to the characteristics of quick speed, sensitiveness and portability, etc., such detecting instrument has now been widely used in military and safety inspection fields. Most of the commercialized portable IMS instruments adopt two sampling methods, that is, solid sampling or wiping sampling, and gas sampling. The former collects particles to be detected by wiping the surface of a suspicious object with a clean sampling carrier, for example, wipe paper, then puts the wipe paper or the sampling carrier adhering with the sample particles to the instrument inlet, and gasifies the solid explosives for analyzing through the method of thermal desorption. During the sampling and testing processes, the operator needs to wear gloves or to use a customized wiping sampler furnished with a sampling carrier in order to avoid polluting the sampling carrier and the detecting instrument. The latter sucks the gas atmosphere or the vaporous sample on the solid surface, which is to be detected, into the sampling device of the instrument for analyzing, via a suction pump directly.
The gas sampling method is easy to operate, no consumable is needed, and it may avoid to directly contacting the object to be detected. However, because the vapor pressure of most objects to be detected, for example, explosives and drugs, is very low (below ppb), it is difficult to reach the lower limit of detection of an instrument simply by the collecting mode of sucking a sample directly. If a preconcentration or preenrichment device is configured on the front end of an analyzing system, the detection capability of the instrument may be improved greatly. A preconcentrator mainly comprises an adsorbing material and a heater, and its operational principle lies in that the gas to be detected is first passed through the adsorbing material for enrichment, and after a certain period of time, the gas absorbed is resolved in a short time by heating the adsorbing material, so that a higher gas concentration may be obtained. Some commercialized instruments, for example, VaporTracer from GE, employ an external portable vacuum suction device for collecting gas samples, wherein a sampling carrier is first placed in the suction port of the vacuum device, and molecules of an object to be detected are captured thereon after an air containing the vapor of the object to be detected is passed through the sampling carrier for a certain period of time, then the sampling medium is placed into the detector and the molecules of the object to be detected are released for analyzing via the method of thermal desorption; therefore, the device actually plays a role of sample enrichment.
At present, there are a plurality of related patents that respectively describe a preconcentration device for an ion migration spectrometer or other analyzing instrument of the same type. U.S. Pat. No. 5,162,652 describes a technology of sample mixing, concentrating and introducing, in which a part of the gas in a sealed luggage is extracted and combined with the ambient atmosphere in a closed cavity, the mixed sample is passed through a collector, and certain molecules to be detected are aggregated onto a collecting surface for concentration, then the molecules absorbed are released from the surface and sent to an ion migration spectrometer for analyzing. U.S. Pat. No. 6,604,406 describes a preconcentration device that can be manually carried, in which an object is captured via a permeable mesh screen, and then the materials of the object are released into a cavity by heating. U.S. Pat. No. 5,083,019 describes an absorbing probe concentration device, in which an absorbing probe made of a metallic filament coil having an absorbing coating is placed in a sampling gas flow at a low temperature, the gas sample is collected via its surface, and during the testing process, the probe is manually fed into a ionization reaction zone of the ion migration device via a slide shaft and then heated rapidly, so that the material to be detected is resolved and ionized. Patent application WO2007091998 describes a concentration technology of solid phase micro-extracting optical fiber collection, in which a solid phase micro-extracting optical fiber exposed in air is employed to collect a sample of explosives, taggants or a mixture thereof, and after thermal desorption, the optical fiber is put into a preconcentration device for concentrating the sample, and then the sample is fed into an ion migration spectrometer for detecting. Patent US20090249958 describes a device component that may replace the concentration carrier, wherein the device component is consisted of a housing and an inner rack, and a cavity that may accommodate several concentration carriers and a channel that accesses to a sampling device of a detecting instrument are formed via a retractable spring compressing device, thus the material collected by the concentration carrier may be brought into the instrument for analyzing via a consecutive gas flow. The concentration device disclosed in patent application WO2008074981 is located inside the ion migration sampling device, a small negative pressure and a small positive pressure are alternately applied to the pipe cavity via a pulse pressure generator connected with the migration pipe cavity, so that an air is sucked into or evacuated from the sampling device in a mode that emulates gasping, thus the component to be detected is effectively absorbed by the preconcentration device, instead of entering the ionization zone, and after the component to be detected is accumulated for a certain period of time, the pressure generator generates a larger negative pressure, so that the object to be detected that is released by the preconcentration device is sucked into the ionization zone inside the instrument for analyzing. The preconcentration device described in patent application WO2007113486 is connected with the inlet of an ion migration spectrometer, wherein the preconcentration device is formed by a metal pipe of which the inner surface has a layer of silastic adsorbing material, and a resistance heating element connected with a power is configured under the absorbing layer for periodically heating the silastic absorbing layer, so that the material absorbed is desorbed and released to an ion migration spectrometer at a higher concentration.
In practical application, because at present, solid wiping sampling is still the sample collecting mode commonly used by the ion migration instrument, a sampling carrier sampling device and a thermal resolver for heating the carrier are often configured on the front end of the instrument. In order not to influence the solid sampling device and the function of the instrument, the concentrator described in the above patents/patent applications (for example, U.S. Pat. Nos. 5,162,652, 6,604,406, WO2007091998 and US20090249958, etc.) generally employs an external design and needs a separate device that is independent of the instrument, and after sample collection is accomplished, sampling is performed in the same mode as solid sampling, thereby the process of the whole detecting operation is made boresome and complex; on the other hand, in an IMS instrument with a built-in concentrator (for example, WO2008074981 and WO2007113486, etc.), because the absorbing element in the concentrator needs to work at a low temperature, no thermal resolver is configured on the front end of the instrument, thus the instrument can only be used for analyzing a gas sample.
Therefore, a more practical IMS instrument that has the functions of solid sampling and gas sampling simultaneously needs to be developed in the prior art. On one hand, it has a built-in concentration device, for simplifying instrument configuration and operation procedure; on the other hand, it may perform a sensitive and facile detection on a trace-amount solid residual and an extremely low concentration gas atmosphere of an object to be detected.